Study of Neutron-Proton Correlation & 3N-Force in 12 C

Transcription

1 Study of Neutron-Proton Correlation & 3N-Force in C Outline: 1. Interesting physics on np-correlations in C 2. Probe: Two-nucleon knockout reaction Partial cross section and P // measurements 3. Experimental setup 4. Preliminary Results 5. Summary Hongna Liu 2 nd International Workshop & th RIBF Discussion on Neutron-Proton Correlations 1 July 7 th, 2015

2 Neutron-Proton Pair Correlations In nuclei: 4 types of Pairs Long-standing open questions: Nature of T = 0 pair in nuclear medium? Relative strength & Interplay of T = 0 & T = 1 np, nn, pp pairs? Long-standing ambitions: Obtaining direct information of T = 0 np pair correlations Isovector (T=1) Relatively Well Described Isoscalar (T=0) A lot of uncertainties! proton neutron Unique N = Z system Valence nucleons move in orbits with identical quantum numbers A dominance of T = 0 over the T = 1 mode

3 Interesting Physics on Neutron-Proton Correlations in C For C pair counting ratio: n p p p~ 2.7 C( e, epn )@4.627GeV Jefforson Lab. (US) High-momentum transfer Short-range correlations Back-to-back n p p p ~ 18 C(p, 3 He), 52 MeV 18 times vs 2.3 times Different Reaction Mechanisms Sensitive to different range of 2N correlations σ-np σ-nn ~ 2.3 M. Yasue et al., JPSJ. 42, 367 (177). R. Subedi et al., Science 320, 1476(2008) C( C, 10 Z)X (Bevatron) E(MeV/u) -pp (mb) -np (mb) (.70) 47.50(2.42) (0.30) 27.0(2.20) (0.2) 35.10(3.40) HI-induced Two-nucleon Results: Knockout n Reaction? p p p~ 5~6 J. M. Kidd et al., PRC 37,2613(18) P. J. Lindstrom et al., PRC 28,1602(138) 3

4 HI-induced Two-nucleon Knockout Reaction C 1 2 Projectile b Target Be/ C surface collision Gain Direct Spectroscopic Information High incident energy Spectator (eikonal reaction model) Core survival and nucleon removal Only affect the nucleon near surface Residues: 10 Be(-pp), 10 B(-np), 10 C(-nn) Cross Section Spatial overlap of the removed two nucleons 0+ Momentum Distribution Total J of the removed pair of nucleons Fig. 1 Calculated P // of 26 Ne after pure π[d5/2] 2 two proton removal from 28 Mg at 82 MeV/u E.C. Simpson et al., PRL 102,132502(200)

5 Observables: Two-nucleon Knockout Reactions from C n n T=1 R s :0.8(0.04) First Calculation: np-removal from C 2.1 C target Sources for the discrepancy? p p T=1 p-shell SM n p T=0&1 R s :0.82(0.04) R s :1.84(0.18) Insufficient T=0 np-spatial correlations in p-shell SM Interaction & Model space? Theory reaches the bottleneck Only Inclusive experimental data For more complete understanding on T = 0 np-correlations More exclusive data is necessary. E. C. Simpson et al., PRC 83, (2011)

6 Observables: np-removal from C Partial Cross Sections Momentum Distributions NCSM +(NN+3N ) NCSM +(NN, w/o 3N ) p-shell SM + WBP Identify indirect reaction process n process P // Measurement E. C. Simpson et al., PRC 86, 05460(20) E. C. Simpson et al., PRC 83, (2011) Verify the np correlations present in SM & Test the role of 3N Force First exclusive measurement of np removal Establish a valuable benchmark

7 Experimental Setup TOF ΔE Be( C, 10 Be) Be( C, 10 B) Be( C, O primary beam: 250MeV/u, ~0.08pnA Production target: Be (5mm) Secondary beam: C 10MeV/u k cps Purity: 7% Secondary target: Be (1.87g/cm 2 ) Beam on Target: 10.7 h BigRIPS PID 11 B 7 13 N C

8 Experimental Setup around SAMURAI Multi-particle Detector Systems BDCs: Tracking of C beam DALI2 (NaI): Gamma rays NEBULA: Neutrons FDCs: Tracking of 10 B, 10 Be, 10 C residues Hodoscope: TOF & ΔE of 10 B, 10 Be, 10 C residues DALI2 SAMURAI Spectrometer Large Acceptance Bρ max / Bρ min = 2 ~ 3 Measured in one setting. Be( C, 10 Be + γ) X Be( C, 10 C+ γ) X Be( C, 10 B+ γ) X

9 Experimental Challenges Higher Trigger Counting Rate Large acceptance Contaminations in the beam ( 11 B) will also be accepted be by SAMURAI. N = Z system A/Q( C)=A/Q( 10 B) Unreacted C beam will be accepted by SAMURAI. Large Background Contamination Empty target run (200 MeV/u & 180 MeV/u) SAMURAI Magnet Apply Hardware Cut to Exclude 11 B & Unreacted C

10 PID without HODP5 PID of Fragments PID of HODP5 10 B Unreacted C was cut off. 10 Be A/Q Resolution Z Resolution 33σ 10σ

11 Inclusive Cross Sections Beam line Detectors FDC1 FDC2 Hodo C Target Background for residues (A/Q 2) SAMURAI C Background for residues (A/Q = 2) Acceptance GEANT4 Reaction loss Transmission of unreacted C Background contamination Empty target runs (200 MeV/u & 180 MeV/u) C( C, 10 Z)X (Bevatron) Be( C, 10 B+ γ) X Acceptance: 2% Reaction loss: 1% Background contamination: 30% Preliminary Results E(MeV/u) -pp (mb) -np (mb) R E(MeV/u) -pp (mb) -np (mb) R (.70) 47.50(2.42) 8.1(13) 10.4(0.2) 37(1) 3. (0.1) (0.30) 27.0(2.20) 5.3(0.5) (0.2) 35.10(3.40) 6(1) J. M. Kidd et al., PRC 37,2613(18) P. J. Lindstrom et al., PRC 28,1602(138) 11

12 Gamma Spectrum of 10 B DALI2: NaI (Tl) Detector Array 15 crystals Angular resolution (FWHM): ~ 8 degree Coverage ( ): 25~154 degree 1 MeV ( = 0.57): 15.4 % Energy resolution 1 MeV : 10.8 % Energy level scheme of 10 B is well studied. (energy & decay branching ratios & life time) Important transitions Simulated Spectrum of 10 B 2154 Important transitions (kev)

13 Gamma Spectrum of 10 B Energy level scheme of 10 B Gamma-Gamma Coincidence Important transitions Gate on 1022 kev Gate on 414 kev

14 Be( C, 10 B + γ) X Partial Cross Sections Add-back Reconstruction was applied to improve the peak-tonoise ratio & photo-peak eff. Fit function: Response functions(geant4) + Exponential background Efficiency from GEANT4:error ~4% All Mγ E level (kev) Incl. J π T (1).3(5) 2.4(2) 3.5(3) 1.7(6) 2.(3) 37 (1)

15 Gamma Spectrum of 10 Be, 11 C, 11 B Be( C, 10 Be + γ) X The partial cross sections in these three reaction channels will be extracted. Be( C, 11 C + γ) X Be( C, 11 B + γ) X

16 Cross Sections from np-removal from C NCSM predicted higher T = 0 cross sections NCSM +(NN+3N ) NCSM +(NN, w/o 3N ) p-shell SM + WBP P // Measurement Preliminary Results Inc. Exp. σ WBP σ NCSM-1 σ NCSM-2 (mb) 37(1) NCSM-1: 2N+3N NCSM-2: 2N+stronger 3N NCSM provides better description of the inclusive cross section.

17 σ -np (mb) Partial Cross Sections from np-removal from C Discrepancy between data and theory (3, 0) (1, 0) Exp. WBP NCSM-1 NCSM-2 NCSM-3N (0, 1) (1, 0) 2N+3N (2, 0) (J, T) 2N+stronger 3N Turn off 3N Exp.: 10 Be Theo.: 2.1 C (2, 1) E (MeV) Theoretical calculations underestimate the cross section to the T = 0 ground state by a factor of 2. The T = 0, np spatial correlations present in the wave functions used are insufficient. NSCM with 3N force provides better description of the data. Signal the importance of 3N force

18 Summary Probe: Two-nucleon knockout reactions from C at 10 MeV/u Be( C, 10 Be + γ) X Be( C, 10 C+ γ) X Be( C, 10 B+ γ) X Inclusive cross sections 1. The inclusive pp- and np- removal cross sections from C show reasonable consistency with previous results. 2. The ratio of inclusive np- to pp-removal cross sections was extracted to be 3.8 (1), larger than the pair counting ratio 2.7. Partial cross sections 1. Theoretical calculations underestimate the cross section to T = 0 ground state by a factor of 2, suggesting insufficient treatment of the T = 0, np spatial correlations in the wave functions. 2. NCSM with 2N & 3N force predicts higher partial cross sections to the first two T = 0 states, and provides overall better description of the data, which signals the importance of the 3N force. 18

19 Collaborators RIKEN J. Lee, H. Liu, P. Doornenbal, N. Inabe, T. Isobe, T. Kubo, S. Kubono, T. Motobayashi, M. Nishimura, H. Otsu, H. Sakurai, H. Sato, Y. Shimizu, H. Wang, S. Takeuchi, K. Yoneda Tokyo Tech. Y. Kondo, N. Kobayashi, R. Minakata, T. Nakamura, S. Ogoshi, Y.Togana Tohoku Univ. T. Kobayashi RCNP, Osaka U. N. Aoi LPC de CAEN J. Gibelin, S. Leblond CNS/ Unvi. Of Tokyo M. Matsushita, D. Steppenbeck Univ. of Kyoto Y. Matsuda R. Minakata Seoul National Univ. J. Hwang Theory Collaboration: Univ. of Surrey J. A. Tostevin, E.C.Simpson LBNL A. O. Macchiaveli, P. Fallon TRIUMF P. Navratil NSCL/ MSU B. A. Brown 1

20 σ -np (mb) Partial Cross Sections from np-removal from C Source of the discrepancy between data and theory (3, 0) Exp. (J, T) WBP NCSM-1 NCSM-2 (1, 0) NCSM-3N Turn off 3N Exp.: 10 Be Theo.: 250 C (0, 1) (1, 0) (2, 1) (2, 0) E (MeV) Ground state: Theoretical calculation dramatically underestimate the cross section to the ground state. Insufficient T = 0 correlations in SM p-shell (WBP) Reproduce the cross sections to T = 1 states. Overall underestimate the cross sections to T = 0 states by a factor of ~2. NCSM (EFT NN+3N) Predicted higher cross sections to the first two T = 0 states. 3N force seems important to explain the data.

21 PID after 2 nd Target PID of Fragments

22 Inclusive Cross Section Preliminary Results 10 B A/Q Resolution 10 Be 33σ Energy (MeV/u) 250 ( C) 65.6(26) 56.0(41) 1.2(0.1) 10 ( Be) 82(2) 62(2) 1.3(1) Energy (MeV/u) 250 ( C) 5.88(.70) 47.50(2.42) 8.1(13) 10 ( Be).4(2) 36(1) 3.8(1) J. M. Kidd et al, PRC 37, 6 (188) Be( C, 10 B+ γ) X Z Resolution 10σ Acceptance: 2% Background contamination: 30% Survival possibility: 81 %

23 Unusual neutron-proton Correlations in C Ratio is Energy Dependent! Higher energy Pick-up pairs with higher relative momentum Larger ΔP Smaller Δx Short range C( e, epn )@4.627GeV Jefforson Lab. (USA) n p p p ~ 18 R. Subedi et al., Science 320, 1476(2008) 1 2 b C( C, MeV/u Target Be n p p p= 6± MeV/u 10 MeV/u 5.3±0.5 3.±0.1 Projectile C J. M. Kidd et al., PRC 37,2613(18) P. J. Lindstrom et al., PRC 28,1602(138) 250 MeV/u C(p, 3 He), 52 MeV n p n p ~ 2.3 M. Yasue et al., JPSJ. 42, 367 (177). Properties of T = 0 interaction at different ranges are determined. Longer range 23